Anti-reflection structure with graded refractive index layer and optical apparatus including same

Abstract

The anti-reflection structure includes a graded refractive index layer that is disposed on a substrate and whose refractive index decreases as a distance from the substrate increases, and a homogeneous layer that is disposed on the graded refractive index layer and whose refractive index is homogeneous. The structure satisfies a condition of nb−na>0.10 where na represents the refractive index of the homogenous layer, and nb represents a homogenous layer side effective refractive index of the graded index refractive index layer.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to an anti-reflection structure that is formed on an optical element as a substrate such as a lens.[0003]2. Description of the Related Art[0004]As a structure that is capable of preventing reflection of light on a surface of an optical element such as a lens and is a structure other than anti-reflection films using an interference effect obtained by a dielectric multilayer film, there is known a structure having roughness (convex and concave portions) in which a pitch of the convex portions is equal to or smaller than a wavelength of entering light. Such a structure is hereinafter referred to as a “minute roughness structure”. The minute roughness structure utilizes a property of light acting on convex portions whose pitch is equal to or smaller than a wavelength of the light as if the structure has a homogeneous effective refractive index.[0005]Such a minute roughness structure is regarded...

AI Technical Summary

Benefits of technology

[0011]The present invention provides an anti-reflection structure having a high mechanical strength of its surface and a high anti-reflection performance, and an optical element and an optical apparatus using the same.

Problems solved by technology

However, securing physical or mechanical strength of the minute roughness structure is difficult, and a surface of the minute roughness structure cannot be wiped because it has roughness.

However, in the minute roughness structure disclosed in Japanese Patent Laid-Open No. 2008-9408, since the space around the convex portions are filled with the porous layer whose refractive index is significantly low, a sufficient mechanical strength cannot be expected.

Moreover, the anti-reflection thin film disclosed in Japanese Patent Laid-Open No. 08-83581 has a sufficient mechanical strength, but does not have a sufficient anti-reflection performance.

The anti-reflection layer provided in the anti-reflection thin film has a low anti-reflection performance only capable of reducing reflection at the electrically-conductive layer, and does not have a high anti-reflection performance capable of preventing reflection at a surface of an optical element.

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